Ultra short wave receiving sets



March 18, 1941.

W I-Pi ULTR SHORT WAVE RECEIVJZNG sE'r' Filed May 28, 1938 I l 1.5 2 2.5 3 l Y A INVENTOR.

ARI/A00 C AMW/A/CKEL Mu-w ATTORNEY.

Patented Mar. 18, 1941 UNITED STATES PATENT OFFICE ULTRA SHORT WAVE RECEIVING SETS Arnaud Cramwinckel, Eindhoven, Netherlands,

assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application May 28, 1938, Serial No. 210,606 In Germany July 5, 1937 3 Claims. (Cl. 250-20) This invention has reference to an ultra-short a resistance II and a condenser ID for setting up radio wave receiving set arranged for the recepa negative grid bias. tion of a predetermined comparatively narrow Fig. 2 shows the substitution diagram of the frequency spectrum and comprising a receiving circuit shown in Fig. 1, the antenna being repre- 5 circuit with attendant doublet antenna. The exsented by an oscillator having an electromotive 5 pression comparatively narrow frequency specforce Ea. and an internal impedance Zs=Ra+jXa trum is to be understood to mean a spectrum the the receiving circuit by its input impedance width of which is smallrelative to the frequencies Ze=Re+iXa The antenna resistance Ra is concomprised within the spectrum. The invention stituted essentially by the radiating resistance relates, therefore, primarily to a fixedly tuned which is heavy as compared with the ohmic re- 10 receiving set, which is only suitable for the resistance. As is well known, the impedance Ze has ception of a single predetermined carrier wave supplied to it a maximum energy when Ra=Ro with attendant side bands, or for the reception of and Xa+Xe=0, that is to say, the energy supthe picture carrier wave and the sound carrier plied to the input circuit of the receiving circuit wave of a single television transmitter. It may, arrangement has reached its maximum value 15 however, be used also with a receiving set which when the input resistance Re of the receiving circan be tuned over a comparatively narrow frecuit equals the radiating resistance Ra of the quency spectrum and which is suitable, for exantenna, and the input reactance Xe is opposed ample, for the reception of two television transto the antenna reactance Xe. In this case, the

mitters whose picture carrier waves have a difinput circuit of the receiving circuit arrange 20 ference in frequency which is small in relation to ment is matched to the antenna. their frequencies. In the receiving circuit arrangements of the The invention has for its object to provide above-mentioned kind hitherto used, the condimeans for obtaining with a given field intensity tion Xa+Xe=0 has always been satisfied by makof the oscillations impinging on the antenna the ing the antenna reactance X8. and also the input 25 highest possible voltage at the control grid of the reactance Xe zero for a frequency comprised withfirst tube of the receiving circuit. in the frequency spectrum to be received, that is In order that the invention may be clearly to say, both the antenna and the input circuit understood and readily carried into effect, it will (5, 6, Fig. 1) have been tuned to the said frenow be described more fully with reference to the quency, the desired tuning of the antenna being 30 accompanying drawing, wherein: obtained in any case by choosing the electric Fig. 1 shows the parts of a receiving set of the length of each of the radiators of the dipole or above-mentioned kind which are necessary for an doublet antenna so as to be equal to one-quarter understanding of the invention; of the wavelength corresponding to the tuning Fig. 2 shows the equivalent circuit diagram for frequency. v 35 the system of Fig. 1; and According to the invention, a substantially Fig. 3 graphically illustrates the relative intenhigher voltage at the control grid of the first sities of input energies available both for a circuit valve is obtained with constant field intensity of designed in accordance with the invention and for the oscillations impinging on the antenna by 40 a circuit according to known practice. choosing the electric length of each of the aerials 40 Referring to Fig. 1 in more detail, the dipole of the doublet antenna so as to be about fiveor doublet antenna comprises two radiators l and eighths of the wavelength that corresponds to a 2, each of which has an electric length Z. The frequency comprised within the frequency spechigh frequency signal oscillations in the antenna trum to be received, the above-mentioned matchare supplied via a double lead 3 to the input coil 4 ing of the input circuit to the antenna being 45 of the receiving circuit which is coupled inducmaintained, that is to say with the said frequency tively to the inductance coil 5 of the input circuit. the input resistance of the receiving circuit is A tuning condenser 6 is connected in parallel with chosen so as to be equal to the radiating resistthe coil 5 and permits the receiving set to be ance of the antennaand the input reactance so as tuned in some cases over a comparatively narto be opposed to the antenna reactance. The in- 50 row frequency spectrum. The voltage occurring vention consists, therefore, in that the antenna is in the circuit 5, 6 is supplied via a grid condenser tuned to a frequency which is about 2.5 times 1 and a leak 8 to the control grid of the first valve lower than with the receiving sets hitherto used 9, e. g., a high frequency amplifier 5. The cathode and the input circuit of the receiving circuit 5 lead of the valve includes in the ordinary manner arrangement is tuned to a correspondingly higher frequency in such manner that the entire receiving set is tuned to a frequency comprised within the frequency spectrum to be received.

The fact that owing to the invention a sub- 5 stantially higher voltage is received at the grid of the first valve than in the well known devices, may be explained as follows: The voltage at the grid of the first valve has reached its maximum value when the energy supplied to the input circuit has reached its maximum value. According to the substitution diagram of Fig. 2, this energy is W=J Re. Now, if the above-mentioned matching conditions are satisfied,

so that If with a constant field intensity, the value a5 is calculated as a function of the length l of T the two doublet radiators, we obtain the curve shown in Fig. 3, from which it is directly seen that for Q a sharp maximum value occurs at which the energy W is about twice as large as for the usual value which is illustrated by the band I2, whereas according to the invention the radiator length Z is chosen, particularly for the average frequency of the spectrum to be received so as to be equal 150 about 4 k, which is represented by the band 13'. As will be seen, the choice, according to the invention, of the radiator length results in a substantially higher energy in the input circuit and thus in a substantiallyhigher voltage at the grid of the first valve.

Instead of a doublet antenna comprising two radiators, as shown in Fig. 1, half a doublet, that is to say a single radiator, may be used whose electric length should also be equal to about fiveeighths of the wavelength of a frequency comprised within the frequency spectrum to be received. This radiator is then connected to one of the conductors of the double lead 3, whereas the other conductor of this double lead is connected to earth.

What is claimed is:

1. An ultra short radio wave receiving set arranged for the reception of a predetermined comparatively narrow frequency spectrum and comprising a receiving electron discharge device circuit coupled to a doublet antenna having two arms, wherein the electrical length of each of the arms of the doublet antenna is about five-eighths of the wavelength that corresponds to a frequency spectrum and for this frequency the input resistance of the receiving circuit is equal to the radiating resistance of the antenna and the input reactance is opposed to the antenna reactance.

2. An ultra short wave radio receiving set arranged for the reception of a predetermined comparatively narrow frequency spectrum and comprising a receiving electron discharge device circuit coupled to an antenna having at least one arm, the electrical length of said antenna arm being about five-eighths of the wavelength that corresponds to a frequency within th said frequency spectrum and for this frequency the input resistance of the receiving circuit being equal to the radiating resistance of the-antenna and the input reactance being equal in value and opposite in sign to the antenna reactance.

3. An ultra short radio wave receiving system arranged for the reception of a predetermined completely comparatively narrow frequency spectrum, comprising an electron discharge device radio frequency amplifier having a control electrode and a cathode electrode, a doublet antenna having a pair of arms each of which has a length approximately equal to five-eighths of the wavelength that corresponds to a frequency within said spectrum, a transmission line coupling said arms to said control and cathode electrodes, the input resistance of said amplifier being equal to the radiation resistance of said antenna, and the input reactance of said amplifier being of opposite sense to the antenna reactance at said fre- 

